Synchronised calvings after withdrawal of norgestomet implants from cows treated near term with prostaglandin.

To investigate whether calving could be controlled by the withdrawal of progestogen implants from cows treated near term with prostaglandin three cows (group 1) received an intramuscular injection of 5 mg flumethasone on day 270 of pregnancy, and four cows (group 2) and three cows (group 3) received implants containing 3 mg norgestomet in both ears on day 262 of gestation and were treated with a prostaglandin F2 alpha analogue on day 264. On day 270 the implants were removed and at the same time the cows of group 3 were treated with 5 mg flumethasone. Jugular blood samples were taken daily to estimate progesterone concentrations in the plasma. Luteolysis was achieved by the injection of prostaglandin, as judged by the decrease in plasma progesterone concentration in the cows of groups 2 and 3 on day 264. Pregnancy was maintained in these cows until after the removal of the norgestomet implants. The interval from the removal of the implants and, or, the injection of flumethasone on day 270 until the onset of second stage labour ranged from 36 to 47 hours and the mean intervals for the three groups were not significantly different. In all the cows except one from group 3 the dilatation of the cervix and vagina and the softening of the pelvic ligaments appeared normal at calving. It is concluded that calving near term can be synchronised by a progestogen in the absence of a corpus luteum.